1. Field of the Invention
In one of its aspects, the invention relates to a vehicular mirror assembly adapted to be mounted to a vehicle for movement between an extended and a retracted position. More particularly, the invention relates to a pivoting mechanism for performing the pivotal movement of the vehicular mirror assembly including a mechanism for reducing the friction within the pivoting mechanism. In another aspect, the invention relates to an external vehicle mirror having both powered folding and powered extension functionality accomplished by a single motor. In another aspect, the invention relates to a shut-off circuit for a DC motor and, more particularly, to a shut-off circuit for a motor contained in a vehicular mirror which performs a movable function for the mirror, such as linear extension or pivotal movement. In another aspect, the invention relates to an extendable vehicular mirror in which the mirror is angularly adjusted upon movement of the mirror between the retracted and the extended positions.
2. Description of the Related Art
External mirrors are ubiquitous for contemporary vehicles. External mirrors have long been used to aid the driver in operating the vehicle, especially in improving the rearward view of the driver. Over time, more and more functionality has been incorporated into the external mirrors. For example, it is common to pivot or fold the external mirror against the vehicle body to prevent the jarring of the mirror when the vehicle is not operated. The mirror-folding function can incorporate a power assist, such as that disclosed in U.S. Pat. Nos. 5,684,646 and 5,703,732, which are incorporated herein by reference.
External mirrors are also extendable away from the vehicle, which is useful when towing a trailer. Mirrors incorporating both the powered fold and powered extension functionality are known and have used separate motors for both the folding and extension functions. Examples of such mirrors are disclosed in U.S. Pat. Nos. 6,276,808 and 6,213,609, assigned to the assignee of the current application, and are incorporated by reference.
The power-assist devices for the mirror-folding function typically include a motor which, upon a suitable activating signal from a controller, drives a rotatable column through an output gear assembly attached to the motor. The rotatable column is operably attached to the mirror so that rotation of the column is translated into pivoting of the mirror. The rotational movement of the mirror is controlled in two ways. The mirror assembly is provided with “stops” which define the outermost and innermost limits of travel of the mirror housing between the extended and retracted positions, respectively, and provide a positive limitation of the pivoting of the mirror. Additionally, the controller actuates the motor for a preset time interval at least equal to the time required to pivot the mirror between the fully retracted and fully extended positions. The motor may thus continue to operate after the mirror has reached its limit of movement defined by the stops. The action of continuing the operation of the motor even after the mirror limit of movement has been reached means that the motor may be forced to work against a virtually immovable obstacle in the form of the stops. In such a case, the current load through the motor will typically increase significantly above the normal operating current, leading to overheating and, eventually, premature motor failure. The increased current load can also lead to overloading and premature failure of associated electrical circuitry, such as the controller, or stripping or other mechanical failure of gears and other mechanical components. Any of these failures will require difficult and costly replacement of the failed parts.
A spring is typically provided around the rotatable column to provide a frictional engagement between the mirror housing and a bracket for mounting the mirror housing to the vehicle (and about which the pivotal movement occurs). This frictional engagement is important to ensure that the rotational movement of the mirror does not overtravel beyond the “stops.” The spring member insures that the rotatable column is held against the mirror bracket so that, when the extended and retracted positions are approached, a positive engagement occurs with the stops.
While the frictional engagement is important at the outermost and innermost limits of travel of the mirror housing with respect to the vehicle, the friction encountered by the rotatable column during the normal range of movement (i.e., between the extended and retracted positions) requires that the motor draw extra current to overcome this friction to move the mirror between the extended and retracted positions.
The trade-off on these types of prior art vehicular mirror pivoting devices is simple. Increasing the friction between the rotatable column and the mirror bracket, while providing a more desirable holding force, requires a more heavy-duty motor to drive the rotatable column, thus increasing cost. Decreasing the friction between the rotatable column and the mirror bracket permits the use of a lower-torque, and thus lower cost, motor but substantially reduces the holding force of the rotatable column against the mirror bracket at the rotatable column pivot to the innermost and/or the outermost retracted and extended positions, respectively.
The mirror may incorporate other power functions such as a motorized tilt mechanism for the reflective element, puddle lights, or turn signal lights. Each of these functions requires electrical connections to the vehicle power supply and onboard controls. Such electrical connections are typically made through a wiring harness which must necessarily pass through the mirror pivot mechanism. The wiring harness must be constructed and routed in order to accommodate the pivoting movement of the mirror. Thus, the wiring harness must have both flexibility to accommodate the pivoting movement and sufficient durability to withstand the repeated pivoting of the mirror assembly. Nevertheless, the repeated flexing of the wiring harness can lead to breakage of individual wires and failure of one or more of the power functions, necessitating costly replacements. Furthermore, the greater the number of power functions, the larger and heavier the wiring harness required, which can add significant weight to the mirror assembly. Finally, fabrication and routing of the wire harness through the mirror assembly can be complicated, requiring additional steps in the manufacture of the mirror assembly, with consequent additional cost.
The use of separate motors for each function is not desirable because it increases costs and part count, which are undesirable characteristics in the automotive parts supply industry. The extra motor also increases the volume of the mirror housing, which is also typically undesirable since increased volume can lead to increased drag, which negatively impacts fuel mileage, and increased wind-induced noise.
Every mirror to be assembled for use on a vehicle does not need to perform the above-listed functions. For example, one mirror may have only a powered folding function. Another mirror may have only a powered extend function. Yet another may have neither. The costs and labor of maintaining multiple designs and assembling different features into a vehicle mirror are often burdensome. There is a need to reduce cost and time in the assembly of vehicle mirrors with multiple functionalities.
When the motor is actuated, typically a rush of current is supplied to the motor as directed by a motor controller due to the momentum required by the motor to move the power-assist devices. At the end of a full range of travel of a power-assist device, the motor is often forced to stop (typically due to a mechanical stop encountered by the power-assist device) but power is still supplied to the motor. If the power is not cut off, the motor can overheat and become damaged. It is also desirable to be able to control a motor that is operable in more than one direction since motors of this type must typically be able to move components in both directions (e.g., between retracted and extended positions).
Current attempts to solve this problem have typically fallen short of a desirable solution. For example, U.S. Pat. No. 6,078,160, issued Jun. 20, 2000, discloses a bi-directional motor control circuit. However, it has been found that this motor control circuit is temperature-sensitive, causing undesirable results when the circuit is used through a wide range of ambient temperatures. It has also been found that a resetable fuse can be provided in series with the motor, however, this arrangement can provide an undesirable recovery time (i.e., waiting for the fuse to reset).
FIGS. 112 and 113 illustrate a vehicle 1310 having a prior art extendable mirror 1312 comprising a base 1314 mounted to the vehicle 1310 with an arm 1316 movable between a retracted position (see FIG. 112) and an extended position (see FIG. 113). A schematic of a driver 1318 is shown in each of FIGS. 112–113 in which the driver's field of view is illustrated by first view field 1320 emanating from the driver 1318 to a mirror 1322 mounted to the arm which, in turn, is reflected and extends therefrom as a second field of view 1324. As can be seen in the extended position shown in FIG. 113, the second field of view 1324 is positioned outwardly of that shown in FIG. 112 due to the extension of the mirror 1322.
This can create a potential “blind spot” as shown by the shaded region in FIG. 113 which could cause the driver 1318 to not be able to see adjacent vehicles, creating a dangerous driving condition. On a more practical level, it can also be annoying for the driver to re-position the mirror manually by either manual manipulation of the mirror 1322 or by using on-board controls (not shown) for repositioning the mirror as is conventionally known in the art.